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Darwin’s “Abominable Mystery”: Mesozoic Cupules Come to the Rescue?

Günter Bechly
Photo: A water lily from the Lower Cretaceous Crato Formation of Brazil, copyright by G. Bechly.

I have been reviewing recent attempts to solve Darwin’s “abominable mystery”: the abrupt origin of flowering plants (see here, here, and here). Another, even newer study by Shi et al. (2021), published in the prestigious journal Nature, claimed to shed light on the mystery (Chinese Academy of Sciences 2021Shah 2021). Soltis (2021) commented in the same journal that with this study a part of the puzzle is nearing resolution. This is highly misleading to say the least.

The authors described several hundred extremely well-preserved seed plant fossils from a 125.6-million-year-old Early Cretaceous peat deposit from Inner Mongolia in China. These fossils exhibit recurved cup-like structures called cupules that surrounded the seeds, likely as a protective layer. These cupules have been speculated to be potential precursors of the outer integument as protective layer (Specht & Bartlett 2009), which is unique to the seeds of flowering plants and the reason for their scientific name angiosperms.

Already on the Scene

As mentioned by Soltis (2021), the newly described fossil plants were contemporaneous with true angiosperms already on the scene. Therefore, they could not have been their ancestors but at best a kind of cousins from an ancestral side branch that survived into the era of true flowering plants. Soltis (2021) leaves no doubt about that:

To be clear, the fossils described by Shi and colleagues do not correspond to the immediate ancestors of flowering plants; those fossils remain to be found.

However, according to Shi et al. (2021) these fossils could be related to much older cupule-bearing Mesozoic plants like the seed fern Caytonia, which already existed since in the early Triassic period around 250 million years ago, right after the great end-Permian mass extinction. Caytonia and its relatives (glossopterids and corystosperms) have been suggested in various phylogenetic studies as putative closest fossil relatives of flowering plants (Doyle 2006Soltis et al. 2008Rothwell et al. 2009), together forming a clade called angiophytes (rejecting the anthophyte clade with the Bennettitales and the genus Pentoxylon, which are recognized as gymnosperms), which is confirmed by this new study.

In my view this new study therefore may indeed enhance our knowledge about plant relationships and potential homologies of the seed covers. But it most definitely does nothing to solve Darwin’s “abominable mystery” of the abrupt appearance and radiation of flowering plants in the Lower Cretaceous period. But what do I know? So I asked a renowned botanist colleague about this new study and here is what he told me:

“Needless to say, it does not solve the abominable mystery, and the homology between the cupule and outer integument is controversial.” Looks like there is not much to see here in terms of mystery-solving.

Failed Predictions

Darwin’s “abominable mystery” has significant implications for the controversy pitting Darwinism versus intelligent design theory. Like every theory, Darwin’s theory makes certain predictions, such as the core prediction of gradualism. Gradualism in this context simply means that all big differences in body plans originated through an incremental accumulation of numerous small changes over long periods of time (Richard Dawkins’s metaphor of “climbing mountain improbable”). This core prediction clearly fails the empirical test of the fossil record, which consistently shows discontinuities and abrupt appearances on all levels in all taxonomic groups and all periods of Earth history. Modern paleontological research and statistical tests of the fossil record have shown, beyond a reasonable doubt, that these ubiquitous discontinuities can no longer be explained away as mere artifacts of our incomplete knowledge of an incomplete fossil record. On the other hand, the empirical evidence perfectly agrees with the predictions from intelligent design theory, which postulates pulses of new information infused into the system from outside and thus leading to saltational changes (with or without common descent).

If Charles Darwin, who was much more cautious in his arguments than his modern disciples, were still alive and could see the modern evidence, I think he would likely agree and would no longer despise such conflicting evidence as an abomination. Even more so would the co-discoverer of the theory of natural selection, Alfred Russel Wallace, who was a proponent of intelligently guided evolution anyway.

So, in a nutshell: Darwin’s “abominable mystery” is not only very much alive and kicking, but it also suggests intelligent design rather than an undirected process of Darwinian evolution as the best explanation for the origin of flowering plants and their unique reproductive organs. What’s true for flowering plants is true for all the other groups of life as well, and even more so for the very origin of life itself.

Postscript: There have been some monosulcate angiosperm-like pollen described from Middle Triassic deposits in Norway and Switzerland (Hochuli & Feist-Burkhardt 20042013). However, such monosulcate pollen are also known from the extinct Bennettitales, which according to the more recent studies rather belong to gymnosperms. Therefore, the attribution of these pollen fossils to angiosperms is highly controversial and disputed by some other leading paleobotanists.

Literature

  • Barba-Montoya J, dos Reis M, Schneider H, Donoghue PCJ, Yang Z 2018. Constraining uncertainty in the timescale of angiosperm evolution and the veracity of a Cretaceous Terrestrial Revolution. New Phytologist 218(2), 819–834. DOI: 10.1111/nph.15011.
  • Bateman RM 2020. Hunting the Snark: the flawed search for mythical Jurassic angiosperms. Journal of Experimental Botany 71(1), 22–35. DOI: 10.1093/jxb/erz411.
  • Bechly G 2021. Botany Journal Revisits Darwin’s “Abominable Mystery”. ID the Future 1420.
  • Bechly G & Meyer SC 2017. Chapter 10. The Fossil Record and Universal Common Ancestry. pp. 331-361 in Moreland JP et al. (eds). Theistic Evolution: A Scientific, Philosophical, and Theological Critique. Crossway Publ., 1008 pp.
  • Bell CD, Soltis DE, Soltis PS 2005. The age of the angiosperms: a molecular timescale without a clock. Evolution 59(6), 1245–1258. DOI: 10.1554/05-005.
  • Bell CD, Soltis DE, Soltis PS 2010. The age and diversification of the angiosperms re-revisited. American Journal of Botany 97(8), 1296–1303. DOI: 10.3732/ajb.0900346.
  • Bridge M 2021. Origin of the quarrel between Charles Darwin and ‘odious’ rival. The Times January 27, 2021.
  • Briggs H 2021. New light shed on Charles Darwin’s ‘abominable mystery’. BBC News 23 January 2021.
  • Buggs RJA 2017a. The deepening of Darwin’s abominable mystery. Nature Ecology & Evolution 1, 0169. DOI: 10.1038/s41559-017-0169.
  • Buggs R 2017b. Darwin’s abominable mystery. Nature Ecology & Evolution Community May 24, 2021(also republished on Richard Buggs’ personal blog).
  • Buggs RJA 2021. The origin of Darwin’s “abominable mystery”. American Journal of Botany 108(1), 1–15. DOI: 10.1002/ajb2.1592.
  • Chinese Academy of Sciences 2021. Dinosaur-age fossils provide new insights into origin of flowering plants. Science Codex May 26, 2021.
  • Coiro M, Doyle JA, Hilton J 2019. How deep is the conflict between molecular and fossil evidence on the age of angiosperms? New Phytologist 223(1), 83–99. DOI: 10.1111/nph.15708.
  • Darwin C 1859. On the Origin of Species … . John Murray, 502 pp.
  • Dawkins R 2009. The Greatest Show on Earth: The Evidence for Evolution. Free Press, 480 pp.
  • Doyle JA 2006. Seed ferns and the origin of angiosperms. Journal of the Torrey Botanical Society 133(1), 169–209. DOI: 10.3159/1095-5674(2006)133[169:SFATOO]2.0.CO;2.
  • Friedman WE 2009. The meaning of Darwin’s “abominable mystery”. American Journal of Botany 96(1), 5–21. DOI: 10.3732/ajb.0800150.
  • Hochuli PA & Feist-Burkhardt S 2004. A boreal early cradle of Angiosperms? Angiosperm-like pollen from the Middle Triassic of the Barents Sea (Norway). Journal of Micropalaeontology 23, 97–104. DOI: 10.1144/jm.23.2.97.
  • Hochuli PA & Feist-Burkhardt S 2013. Angiosperm-like pollen and Afropollis from the Middle Triassic (Anisian) of the Germanic Basin (Northern Switzerland). Frontiers in Plant Science 4, 344, 1–14. DOI: 10.3389/fpls.2013.00344.
  • Li HT, YI TS, Gao LM et al. 2019. Origin of angiosperms and the puzzle of the Jurassic gap. Nature Plants 5, 461–470. DOI: 10.1038/s41477-019-0421-0.
  • Meyer SC 2013. Darwin’s Doubt. HarperOne, viii+498 pp.
  • Nelson P & Klinghoffer D 2016. Scientists Confirm: Darwinism Is Broken. CNSNews December 13, 2016.
  • Oskin B 2015. Controversy Blooms Over Earliest Flower Fossil. LiveScience 08 April 2015.
  • Rothwell GW, Crepet WL, Stockey RA 2009. Is the anthophyte hypothesis alive and well? New evidence from the reproductive structures of Bennettitales. American Journal of Botany 96(1), 296–322. DOI: 10.3732/ajb.0800209.
  • Sawal I 2021. Flowering plants may be 100 million years older than we thought. NewScientist 28 January 2021.
  • SciNews 2021. Study: First Flowering Plants Appeared in Jurassic Period or Even Earlier. SciNews Feb 9, 2021.
  • Sgorbati S, D’Antracolli M, Citterio S, Gentili R, Peruzzi L 2018. Was Charles Darwin right in his explanation of the ‘abominable mystery’?. Italian Botanist 5, 25–30. DOI: 10.3897/italianbotanist.5.24699.
  • Shah K 2021. Fossils of extinct plants reveal origins of today’s flowering species. NewScientist 26 May 2021.
  • Shi G, Herrera F, Herendeen PS, Clark EG, Crane PR 2021. Mesozoic cupules and the origin of the angiosperm second integument. Nature 26 May 2021, 4 pp. + Extended Data. DOI: 10.1038/s41586-021-03598-w.
  • Silvestro D, Bacon CD, Ding W, Zhang Q, Donoghue PCJ, Antonelli A, Xing Y 2021. Fossil data support a pre-Cretaceous origin of flowering plants. Nature Ecology & Evolution 5, 449–457. DOI: 10.1038/s41559-020-01387-8.
  • Smith SA, Beaulieu JM, Donoghue MJ 2010. An uncorrelated relaxed-clock analysis suggests an earlier origin for flowering plants. PNAS 107(13), 5897–5902. DOI: 10.1073/pnas.1001225107.
  • Sokoloff DD, Remizowa MV, El ES, Rudall PJ, Bateman RM 2019. Supposed Jurassic angiosperms lack pentamery, an important angiosperm-specific feature. New Phytologist 228(2), 420–426. DOI: 10.1111/nph.15974.
  • Soltis DE 2021. Ancient seeds spill secrets about the evolution of flowering plants / Seed for thought. Nature News 26 May 2021, 2 pp. DOI: 10.1038/d41586-021-01347-7. [PDF]
  • Soltis DE, Bell CD, Kim S, Soltis PS 2008. Origin and Early Evolution of Angiosperms. Annals of the New York Academy of Sciences 1133(1), 3–25 . DOI: 10.1196/annals.1438.005.
  • Specht CD & Bartlett ME 2009. Flower Evolution: The Origin and Subsequent Diversification of the Angiosperm Flower. Annual Review of Ecology Evolution and Systematics 40(1), 217-243. DOI: 10.1146/annurev.ecolsys.110308.120203.
  • University of Bristol 2021. New study unravels Darwin’s ‘abominable mystery’ surrounding origin of flowering plants. News and features 28 January 2018 (e.g., also in Science Daily January 28, 2021).